


Sensei Oshiete Kudasai!

by airyblueberry



Category: IDOLiSH7 (Video Game)
Genre: Dirty Talk, Incest, M/M, Shameless Smut, Sibling Incest, Studying, if it's counted??, izumicest
Language: English
Status: Completed
Published: 2018-09-15
Updated: 2018-09-15
Packaged: 2019-07-12 16:49:22
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 2,439
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15999347
Author URL: https://archiveofourown.org/users/airyblueberry/pseuds/airyblueberry
Summary: Iori needs to revise for his biology test on human reproduction.Mitsuki has a less than conventional way of helping him.





	Sensei Oshiete Kudasai!

**Author's Note:**

> i apologise in advance

Soft moonlight filtered into the younger Izumi’s room, as he was silently writing down notes for his upcoming biology test. It encompassed content from earlier about the reproductive systems.

He frowned. It was taking longer than expected to memorise everything. The younger Izumi brother sighed as he picked up his notes again, forcing himself to commit the definitions and functions on his notecards into memory while ignoring the stinging bright light of his desk lamp.

He heard a knock on the door. Iori turned. It was three in the morning, who could possibly be awake?

He placed a hand on the door handle and opened the door. “Please refrain fr---”

“Iori…!” whined the person on the other side, Mitsuki Izumi. The other must have noticed his light on under the door. “What are you doing up so late? We’ve gotta be at our best mental state tomorrow for our interview!”

Iori frowned. He really didn’t want to think about it. “I have a biology test next Monday, I need to study first,” he explained. “I won’t have time for it if I don’t finish this chapter tonight.”

“Hm? What chapter is it?” Mitsuki asked. “I was pretty good at biology. You can ask your reliable Nii-san for help!”

“Ah but…” Iori mumbled. He didn’t want to impose on his brother. But the help would be nice… “The chapter is the one on human reproduction.”

The younger Izumi brother could feel his cheeks warm slightly as he explained his situation. Studying the reproductive system made him think about his Nii-san, and how adorably proud he was of his biology marks when he was younger, but also about how he wanted the other. About the late nights Iori spent thinking about Nii-san in such a sinful, decadent way that he’d have to take a cold shower the next morning so that he could concentrate in school.

Mitsuki hummed, a small smirk appearing on his face. “Nii-san can show you a different way to learn that...”

Mitsuki started to run his fingers down the younger brother’s arm, intertwining their fingers. Iori’s face burnt up more, blood rushing downwards as the other teased him. It sent a shiver down his spine, with how forward his brother can be.

“N-Nii-san...?”

Mitsuki chuckled, holding Iori’s hand. “Well, is that a yes?” he asked.

Iori contemplated for a second. He realised that this was a scandal upon a scandal. A sin within a sin. It could mess up IDOLiSH7 if it ever got out…

“Yes.”

Mitsuki hummed, tugging the other out of his room as he snagged his flashcards before going out the door and into the elder Mitsuki’s room. He waved to Nagi in the dining room, who was writing answers for an interview and scaring the hell out of Iori. There were people awake in the dorms?! Though it didn’t matter, Mitsuki’s room was soundproofed since he had Nagi’s speakers there. In fact, that’s the reason why their most explicit indulgences occurred there.

Mitsuki closed the door and pulled Iori to his bed, nearly tripping over his coffee table in the process before pushing Iori down by his shoulders, causing Iori to shout in shock.

Mitsuki took a bit of time to admire the look on Iori’s face. His cheeks were a bright red as the older brother overshadowed him, an expression of flusteredness and embarrassment etched into the other’s sharp features.

“My little brother is so adorable…” Mitsuki hummed, running his warm hands up and down the other’s double flat jacket. He sat up and licked his lips, before slowly dragging the zipper down. “I wanna see more and more…”

“Ah, Nii-san..” Iori mumbled, the weight moving to nearer his lower regions, making him blush. “Wasn’t this supposed to be about studying?”

Mitsuki flushed a little, a small smile appearing on his face. “E-Eh? Well, this is my way of studying biology.”

Iori grumbled a little, moving a hand to his face to try and hide his blush. “Nii-san...that’s dirty…”

Mitsuki smirked softly, taking Iori’s wrist and yanking it away. “My little brother is so cute...does it matter if it's dirty?” he hummed, before leaning in and kissing the younger Izumi, smashing their lips together in a messy, heated fashion and effectively muffling the embarrassed comment Iori was about to make.

Mitsuki hummed deeply, pushing his tongue inside as he ran his hands downward again, running his hands down Iori’s slim waist under his shirt before approaching the other’s soft pyjama pants. He pulled away to waistband before letting it smack against his skin. Iori’s mouth fell open with a quiet moan. The younger brother was already so riled up, just by watching the older play.

Mitsuki pulled away, a strand of saliva breaking as they stared into each other’s eyes for a moment. They were panting, catching their breaths.

Mitsuki smiled, reaching for Iori’s growing bulge in his pants. “Hmmn...you really want this, huh? How naughty...” He gripped it, making Iori moan embarrassingly. With a chuckle, Mitsuki continued. “Good little boys don’t get horny while studying...”

Mitsuki licked his lips, slowly pulling the soft fabric down, along with Iori’s boxers. “So, my _naughty_ Iori,” he started. “Can you tell me how you got this way...?”

“I-I…” Iori mumbled. His face bright red as he tried to collect his thoughts. “Blood...fills the soft tissues i-in there...”

Mitsuki hummed, satisfied. “Correct…”

He pulled the article of clothing off, releasing Iori’s shaft from the soft fabric cage. It was already leaking precum, the transparent beads of liquid seeping from the slit. “Hmmn...you’re so wet, Iori…” Mitsuki hummed, leaning in to kiss the tip of his dick. “Is this making you needy? Do you want Nii-san to go faster?”

Iori squirmed a little, whimpering with the warm breath hitting his straining shaft. The soft breath making him _squirm_ .“Y-Yes...Nii-san.”

Mitsuki smiled, pulling a drawer open and fetched a bottle of lube. He was also hard by now. Mitsuki groaned frustratedly- he really wanted to shove Iori into the bed and show him a good night. However, he was determined to keep it up. He coated his fingers with the lube, coaxing Iori into more of a sitting position as he started to kiss his younger brother’s neck.

Iori whimpered, his thighs shaking a little as the other started to pleasure him more giving in to his needs. “Hah...Nii-san…!” he keened, turning his head to give his Nii-san more room.

“Iori,” he whispered into the other’s ear and making him shudder. “Can you tell me which hormone is making your dirty, _dirty_ body feel this way…?”

“H-Hmmn..! Nii-san, that’s s-so..” Iori whimpered, bucking his hips up into the other. “I-It’s testosterone, r-right?”

Mitsuki sunk his teeth into Iori’s flesh, making the other gasp pleasurably, almost as a reward. “Good boy, Iori...” he hummed.

Mitsuki pulled his fingers out, running one of his fingertips up the younger brother’s member, before wrapping his hands around it and starting to pump.

“H-Hh….” Iori panted, turning his head to the side and concealing the other half. His head was _swimming_ with the increasing intensity Mitsuki was using. Mitsuki was sending waves of euphoria down his thighs, like he was electric. And each touch was burning down his body and  _bringing him to shambles._

Mitsuki moved lower, trailing searing kisses down Iori’s stomach and admiring the shaking muscles underneath his lips. Iori was slim, but toned with how much he keeps up with his health and how hard he tries at PE lessons in school.

“So beautiful, Iori,” he teased, sinking his teeth into the other’s hip.

“N-Nii-san!” Iori protested, biting his lip as he resisted the urge to buck his hips up into Mitsuki’s mouth, to urge him to stop teasing him already. He almost forgot that this was supposed to be about studying.

“Hmm?” Mitsuki asked innocently, before shifting a little between the younger one’s thighs and sucking the flesh there. “What’s the matter…?”

“H-Hnaaah!” Iori moaned, nearly closing his thighs before Mitsuki pushed them apart. “N-Nii san, please stop f-fooling around…!”

“Ahhh...since you asked so nicely…” Mitsuki replied, before beginning to mouth at Iori’s shaft and grabbing what was underneath. He never actually took it in, just lapped at the dripping precum that was starting to leak onto his bed.

“G-Ghh…! Ah…” Iori gasped. He felt so submissive. He didn’t care anymore, not with how deliciously good Nii-san could make him feel, with the surges of pleasure flowing through his thighs.

“Iorin,” Mitsuki called, pulling away fo only a second. “What’s the purpose of these parts...If you get it right, I’ll reward you handsomely…”

“H-Hnnn...N-Nii-saaan…” Iori panted under his breath. “T-The purpose is t-to---mmph!---is to..d-dispense sperm i-into a woman a-and to produce...mmh..!”

“Come on, Iori,” Mitsuki hummed before sucking on the tip, drawing out weak mewls from his brother. “You can do it, my clever little brother…”

“T-To...produce s-sperm and t-testosterone…” Iori finished before releasing the moan he had been holding back as he was answering.

Mitsuki let out a hum of praise. He was falling for Iori...all those sweet whimpers and hot breaths were driving him absolutely _insane_ for his little brother. He couldn’t resist the reward he was about to give…

“I did promise you a reward…” Mitsuki hummed, using every bit of his willpower to maintain his salacious persona. “Come closer, Iori. And lie down.”

Iori did as told, shuffling shyly towards Mitsuki and lying down on his back. He could anticipate what was to come, and he knew just how shameless he had to be, if he let the other continue...but his own head was swimming with lust, his logic muddled with wanton _desires_. He wanted, no, _needed_ his Nii-san…

He supposed, he didn’t care. Not now.

“Good boy, Iori” Mitsuki hummed, dragging out the syllables’ in his brother’s name. Before crawling over him. Mitsuki stretched him again with his fingers for a bit, scissoring to ensure that Iori will be safe. “That’s all of them correct so far…”

He crawled on top, moving his hands underneath Iori’s neck to pull him closer as he carefully pushed himself inside.

Iori mewled, burying his face in Mitsuki’s shoulder as he carefully inserted himself, listening to his older brother’s gentle praise of You’re doing so well.

“Can I move now?” Mitsuki hummed, licking at Iori’s neck. In contrast to his smooth words, his thighs were practically shaking with how much he wanted to plow into his little brother like a filthy wolf.

Iori nodded softly, still hiding his face in his Nii-san’s shoulders and mentally preparing himself from what he knew would be an onslaught of ecstacy…

Mistuki chuckled, almost darkly, making the younger Izumi quiver. He eased the other off of his shoulder for ease, before kissing the other deeply again, and starting to pump, swallowing the moans and sighs of the younger Izumi in a lustful liplock.

The other pushed in at different angles for a bit, humming his praises to Iori before the younger brother whimpered loudly, breaking the kiss.

“N- _Nii san…!_ ” Iori gasped, the surges of pleasure driving him up the wall. “T-Th-- _ahn._.! That feels _s-so_ …” The younger Izumi brother could barely think his usually rational thoughts as the other pounded his shaft into a sweet spot deeper inside.

MItsuki smiled with satisfaction. “Can you remember the function of the part I’m hitting right now, Iori?”

“I-I…! _Mmph_!” Iori gasped, his mouth falling open as he covered his mouth with his hand to stifle his embarrassingly lewd noises. His elder brother merely pulled it away by the wrist.

“You can’t do that, Iori.” He scolded gently between moans. “You still need to answer your Nii-san...”

“Ah... _H-Haah!_ ” Iori moaned, the saliva he was forgetting to swallow starting to leak out the corner of his open mouth. “U-Uh...s-shit…!”

“Iori~ D-Do you know the answer?” Mitsuki hummed into his younger brother’s ear as he pushed his cock in particularly hard, groaning delightedly. “Or...do I need to remind you?”

Iori racked his brains for the answer, but every time he tried to recall the definition he wrote down in his notes, another shot of pleasure surges through his thighs, like alcohol burning its way down someone’s throat, effectively interrupting him.

“T-The prost--- _mmph_!----stores..ah…” Iori moaned. “I-It uh..! It secretes f-fluid with---H-Haah! _N-Nii san…!?_ ”

Mitsuki was now sucking on the base of Iori’s neck, bending a little so the older brother can reach the softer spots on the side of the younger’s neck. “Hmm? What’s...hah...wrong?”

“ _G-Gaa...h_...you’re--mmph! M-Making me feel so...too  _good_ …!” Iori panted, _shuddering_ as his Nii-san pushed right into that spot again. “I-I’m gon--haaah!-- I-I’m gonna cum…! _N-Nii-san…!_ ”

“T-That’s the point, Iori...” Mitsuki stuttered. “Nii-san wants you to f-feel so, _so_ good…”

Mitsuki hummed again, the noise vibrating deep in his throat as he grabbed his younger brother’s thighs, spreading them open wider.

Iori would’ve turned even redder if he could, with the shame of how lewdly positioned he was. Though, he wanted to display himself for Nii-san, a deep ache to be his and _only_ his.

Iori made a lewd sound with every hard shove Mitsuki did. He was practically screaming with how intense Mitsuki was pleasuring him. His normally calm and collected demeanor was absolutely gone, having been torn to shreds by the pure pleasure of his beloved Nii-san.

“N-Nii saaaaaaaan!” Iori cried out, letting his eyes roll back into his head for a second before letting them flutter close, his eyebrows turning up. “ _Mooore_ , more, please!”

Mitsuki cursed under his breath. The other felt too damn good, with his slick, tight walls clenching around his member, with the hot cries of “Nii-san!” leaving his drooling lips. Mitsuki could just drown. He grabbed the other’s member and pumped, furiously jacking the younger IDOLiSH7 member as his breaths grew louder.

_“Ahhhhhh! F-Fuck…!”_

Iori came instantly, the white substance spilling all over Mitsuki’s hand as the other came inside Iori with a deep groan. Mitsuki flopped onto Iori’s stomach, panting as they caught their breaths and composure, regaining their normal selves.

“N-Nii san…” Iori panted. “T-That….”

“Haah...was it good, Iori?” Mitsuki asked, pressing gentle kisses to Iori’s flushed cheeks. He almost had to take a picture. Iori’s beautifully sharp, grey eyes were glassy with that post-sex high. Pale skin marked with flush, darkening hickeys and streaks of cum. Mistuki wished he could take a picture of such a _perfect_ sight. 

 

“I-I…” Iori breathed

“I’m never gonna look at my notes the same way again.”

**Author's Note:**

> hhhh!! it's done!!
> 
> anyway, this is pretty much my first ever fanfic, so i hope it was to people's liking! please comment if you spot any typos or missing tags.
> 
> thanks a lot to my friends who helped me beta and edit www


End file.
